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doi:10.2204/iodp.proc.347.106.2015

Operations

Transit to Hole M0062A

Operations in Hole M0061C were completed at 1220 h on 5 October 2013. The vessel then awaited the arrival of a pilot at 1600 h before transiting to Hole M0062A (proposed Site BSB-11).

Hole M0062A

The vessel arrived on site at 1810 h on 5 October 2013 and commenced operations, having built the dynamic positioning (DP) model (Table T1). The uppermost 0.5 m was not cored because of the potential presence of harmful contaminants associated with historic paper mill outputs. In accordance with the risk assessment, additional personal protective equipment (PPE) was worn for the first core runs at this site.

Eleven piston cores and one hammer sample were collected at this site on 5–6 October. As at Site M0061, the end of the hole was called when drilling encountered the sand lithology underlying the varved sequence. In this hole, the operation was terminated at 35.90 meters below seafloor (mbsf), and the vessel prepared to move over to Hole M0062B.

A total of 12 coring attempts were made in Hole M0062A, along with one open-hole section at the surface (to avoid coring contaminated sediments). The maximum hole depth was 35.90 mbsf with a recovery of 97.41% (inclusive of the open-hole 0.5 m) and 97.82% when the open-hole interval is removed from the calculation.

Hole M0062B

The vessel established position over Hole M0062B at 0423 h on 6 October 2013. The noncoring assembly (NCA) was again used for the uppermost 1 m because of the potential for contamination and to establish the offset between core runs required to produce a composite stratigraphy for this site.

Piston coring ran smoothly throughout 6 October using seawater as the drill fluid. The hole ended at 24.10 mbsf in silty material.

A total of seven cores (and one 1 m NCA section) were attempted in Hole M0062B. Hole recovery was 98.57% when the open-hole section is discounted.

Hole M0062C

After coring Holes M0062A and M0062B, it was possible to reassess the risk of coring contaminated sediments. It was evaluated on board whether any risk from collecting a surface piston core could be mitigated and decided that scientifically it would be beneficial to provide this uppermost interval.

One core was collected from this hole. This core recovered 3.43 m of sediment from a 3.3 m run, indicating expansion.

Hole M0062D

At 1000 h on 6 October 2013, the vessel established position over Hole M0062D. The uppermost 1.5 m of sediment was not cored in order to establish the offset between core runs required to produce a composite stratigraphy using all holes at this site. The NCA was initially used before switching to the piston corer system for the remainder of the hole. The first core was recovered to deck at 1025 h. Coring ran smoothly on 6 October, and the final core was recovered to deck at 1405 h, after which the drill floor was prepared for downhole logging.

Downhole logging operations were run by the Petrophysics Staff Scientist and the Weatherford Engineer and Technician. Setup for logging operations was complete at 1535 h, and the first tool string was run shortly afterward. The string consisted of the compact gamma ray and compact induction tools. The first uplog began at 1600 h, and the tool reached 9.50 mbsf, when the string lost tension. The tool was recovered to deck at 1610 h. The second logging run involved the compact gamma ray and compact spectral gamma tools and was run into the hole at 1625 h. Again, the string lost tension at 9.50 mbsf and the uplog began at 1634 h. The tool was then recovered on deck. Because of the short section of hole that remained open for logging, logging operations ended after this run, and the vessel prepared for transit to Site M0063.

Seven cores were recovered in this hole to 21.0 mbsf, with a recovery of 100%. An open-hole section of 1.5 m was drilled.

Holes M0062K and M0062L

Two Rumohr cores were also collected at this site on 6 October 2013, following a reassessment of the potential risk from coring contaminated sediments in the upper 50 cm. The corer was deployed over the starboard side of the vessel using a system of winches. The corer recovered 0.95 m (Hole M0062K) and 0.92 m (Hole M0062L) of sediment. In order to mitigate any risk from contaminated sediment associated with the historical paper mill industry, additional PPE was used by those involved in acquiring the Rumohr cores. The Rumohr corer and outside of the liner were pressure washed prior to being brought onto the vessel to remove as much potentially contaminated material as possible. All equipment and PPE were also thoroughly washed after use. The cores themselves were labeled and sealed in black bags for transport back to the IODP Bremen Core Repository (Germany).